The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise quality as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An ever-increasing number of relatively inexpensive, low power wireless data communication services, networks and devices have been made available over the past number of years, promising near wire speed transmission and reliability. Various wireless technology is described in detail in several IEEE standards documents, including for example, the IEEE Standard 802.11b (1999) and its updates and amendments, the IEEE Standard 802.11n, as well as the IEEE 802.15.3 Standard (2003) and the IEEE 802.15.3c Draft D0.0 Standard, all of which are collectively incorporated herein fully by reference.
As one example, a type of a wireless network known as a wireless personal area network (WPAN) involves the interconnection of devices that are typically, but not necessarily, physically located closer together than wireless local area networks (WLANs) such as WLANs that conform to the IEEE Standard 802.11a or the IEEE Standard 802.11n. Recently, the interest and demand for particularly high data rates (e.g., in excess of 1 Gbps) in such networks has significantly increased. One approach to realizing high data rates in a WPAN is to use hundreds of MHz, or even several GHz, of bandwidth. For example, the unlicensed 60 GHz band provides one such possible range of operation.
As is known, antennas and, accordingly, associated effective wireless channels are highly directional at frequencies near or above 60 GHz. In general, path loss on a wireless communication link may be partially determined by such operational parameters as carrier frequencies and distances between communicating devices, and may be further affected by shadowing effects along transmission paths, channel fading due to reflection, scattering, oxygen absorption, etc., and other environmental factors. As a result, link budget (i.e., the aggregate of gains and losses associated with a communication channel) is frequently subject to a significant path loss.
When multiple antennas are available at a transmitter, a receiver, or both, it is therefore important to apply efficient beam patterns to the antennas to better exploit spatial selectivity and improve the link budget of the corresponding wireless channel. Generally speaking, beamforming or beamsteering creates a spatial gain pattern having one or more high gain lobes or beams (as compared to the gain obtained by an omni-directional antenna) in one or more particular directions, with reduced the gain in other directions. If the gain pattern for multiple transmit antennas, for example, is configured to produce a high gain lobe in the direction of a receiver, better transmission reliability can be obtained over that obtained with an omni-directional transmission. In addition to providing better link reliability, beamforming can greatly reduce the amount of power dissipated by transmitting devices. More specifically, beamforming allows a transmitting device to focus the transmission power in a particular direction when transmitting data to one or several receiving devices.
Example beamforming techniques are described in commonly-owned, co-pending U.S. patent application Ser. No. 12/548,393, filed on Aug. 26, 2009, and entitled “Beamforming by Sector Sweeping,” which is hereby expressly incorporated by reference herein, and in the commonly-owned, co-pending U.S. patent application Ser. No. 12/562,782, filed entitled “A New Digital Beamforming Scheme for Phased-Array Antennas,” filed on Sep. 19, 2009, also expressly incorporated by reference herein.